Method of providing alloy contacts on semi-conductor bodies



Jan. 5, 1965 E. KOO] OVIDING ALLOY CONTACTS Filed Sept. 12,

ON SEMI-CONDUCTOR BODIES FIGA FIG.5

ELSE KO Y .iwe. 2.

AGENT tems, such as'transistors anddiodes.

, during the alloying hesive'itself. Q

,numerals.

InFlGURE 1, a semi-conductorbody 1, consistingof p-type germanium, hasits upper surfacecovered with a layer 2 0i an adhesivelf This layer maybeprovided by dipping ,the body into acne-half percent solution ofneatfs foot oil-"(oleum pedum tauri) in acetone, After extract- 7 ingthe body from the solution the surface ,of the body. is covered with alayerof the'solution, havingIathiclQ' "ness of about lfiflinicrons, fromwhich the solvent evapo United" StaeSPatmfO METHOD OF PRQVIDXNG ALLOYCGNTACTS 0N SEMl-CGNDUCTOR BGDIES Else Kooi, Eindhoven, Netherlands,assignor to North American Philips Company, Inc, New York, N.Y., a

corporation oi Delaware Filed Sept. 12, 1961, Ser. No. 137,606

Claims priority, application Netherlands Sept. 13, 1960 6 Claims. (Cl.148-179) The invention relates to a method of providing alloy contactson semi-conductor bodies, in which method p'ellets of the alloyingmaterial are arranged so as to engage 'a semiconductor body by means ofa jig having apertures in each of which sucha pellet is disposed afterwhich the pellets are alloyed to the body,

The expressionpellets as used herein is not restricted to bodies ofsphericaltshape but alsoincludesother appropriate shapes, for example,disc-shaped filamentary bodies. The above-mentioned known method isused, for

example, for manufacturing semi-conductive electrode, sys- 1 It is knownto arrange the pellets in a jig'so as to engage the body and then toheat the whole to the alloying temperature. It is'also known to arrangethe pol-- lets in a jig so as to engage the bodyfto fuse them to thebody at a low temperature, after which the jig isre'moved and the actualalloying process is carried out without the use of a jig. it has beenfound been found that the'molten alloying material tends to that thepresence of the jig'in the fusingand, as the case may be, alloyingprocesses may 1:; give rise to the introduction of impurities. It hasalso adhererto the jig. Consequently, thechoice of the mal Yterial ofthe jigs is restricted to materials which are not readily wetted andevolve little impurity, such as graphite and stainless steel.

It is an object disposed in the jig are stuck to the, send-conductorbody by means'of an-adhesivepafter which the jig is removed and thepellets are alloyed'to the body. During the use ofthejigno heatne edbeapplied. f r i of the invention to obviate these, disadvantages.According to the invention, thepellets while hesive disappears.

A The bodyand pellets fused to it'may be treated further :PatenidJ n. 5,.1965

having a diameter of 45 microns, are disposed, f.i., by

rolling over the jig 4, so as to adhere to the semi-conductor body 1 bymeans of the adhesive of the layer 2 (FIGURE 3). Between the jig 4 andthe body 1, a slight spacing 7 is permissible. However, this. spacinghas to be smaller than the diameter of the pellets 6 so that the lattercannot find their way into the interstice between'the jig and the body.By this spacingthe jig 4 is prevented from adheringto the body 1. n Theplate-shaped jig 4 is now removed from the holder --3. Thebody 1 can betaken from the'holder 3,'--the pellets 6 remaining in position (FIGURE4), also when the body is turned upside down'withthe pellets hangingunderneath the body. i r

The semi-conductor body 1 is now heated, for example in a conventionalfurnace, using a'hydr-ogen atmosphere or other inert atmosphere," to atemperature of about 500 forjabout 2 minutes to fuse the pellets 6 tothe body 1 (FIGURE. 5).

in the manufacture of atransistor, forinstance in the Tollowingway,known per se,'added, for the sake of completeness, but in-itself notimportant for the underlying invention.

aluminum dissolving in' the molten. material of fsaid one pellet andarsenic partly diffusing from the molten pellets into the body, partlyevaporating and difiusing in the ex- Preferably an adhesive is usedwhich consists fofa material which is volatilizedlduring'the fusingprocess,

for example an-oil produced. as a distillate. Q-The adhesive preferablyalso contains aflux toensure satisfactoryiwjetfi ting of the surface ofthe body by the alloying rnaterial-"" process. This flux may-be the Themethod in accordance" with invention iswparticularly suited forproviding alloy contactsjcontaining gallium on semi-conductorbodies."Galliumjand gallium alloys whenmolten havethe property ofadheringitofsub f stantially any solid materialwith which theycor'neinto Contact. i -1;? 1 if "In order that the invention maybe readilycarried out, i l

an embodiment thereof will'now bel'describ'ed morefully, byway ofexample,with'reference to. the accompanying" diagrammatic drawing, thefigures 'ofwhich arevertical posed surface parts-of the bodyfor'ming ann-type surface layer. 'When cooling down, firstly germanium, dissolvedin the: molten" material ofthe pellets by the heat treatmenhsegregatesonto the undissolved germanium of thebody after which the rest of thematerial of-the pellets solidifies, on top or the segregatedlayers. Inthe case of fsaid' one pellet containing aluminum, the segregated layerispftypq'formi'ng a p n-junction with the n-type layer, formed bythe-diffusion of arsenic. In theficase of; the

otherg-pellet thefsegregated layer is ni-t ype. After removing'i'tlie'n-type surface 'lay'er-frorn the side of the body iopposi-teto thepellets, andattaching aj'hicliel tablt'o said side by means of a solderconsisting offindium. and gallium'aiid attaching tinned fwire s to'thepellets, p n p-transistor is formed in which 'the ni'ckel tab forms thecollector-connection, thesaidone" pellet forms-the emitterj'eleotr'ode-and the other pellet forms the base electrode; 7

sectional views of variousstagesofaprocess of providing 77 alloycontacts on a semiconductor-body; In the figures, like components aredesignated 'by the same reference" Thefsinglfe jig 'describedhereinbefore may obviously ;-b e replaced-by amultiple jig for providingpe'lletsonsev- Y Qeral semiconductor bodies; Alternatively, severalplate;

shaped jigs may be employed with a holder containing oneor severalsemhconductor bodies.

lnstead pf eats-foot oil many other adhesivesrr'iay;

v be used, .for"ex'ample other oils, greases and fats, prefer-w ablyapplied as a solution in a solvent, rapidly evaporating J- ;I atroomteniperatures,*suchthat an extremlythin layer a i of the adhesive may beformed. .70

As a few examples of suitable solvents out ofmany possibilities, "we maymention acetone -for' po'lyalcohols,

' vegetable and animal oilsand fats, methanol for polyalco- Duringthisheat treatment, the ad- I one; pellet a small dot of paint is applied,and the body is heated to a temperature bf 700C. for two 'hours,:thepellets being remelted,

hols, such as glycol and glycerol, which are also suitable adhesives andtrichlorethene for mineral oils, greases and.

fats. For instance in a modification of the above example a one-halfpercent solution of liquid paratfin in trichlorethene was used. Theadhesives may preferably be chosen such that they will evaporateentirely on heating. So oils are preferred over fats and greases.

Mostly very diluted solutions of the adhesives, f.i., up to 1%, aresuitable as normally very small pellets, f.i., up to 200 microns, areused in the manufacture of semiconductor electrode systems. However,when using substantially large pellets more concentrated solutions maybe chosen. Y

To the adhesives fluxes may be added, f.i.', in finely divided form, orif possible it may be dissolved in the adhesive or the solvent; in thelatter case the flux may segregate in a finely divided state, mixed withthe adhesive after the evaporation of the solvent. Well-known fluxes maybe used such as zinc chloride, indium chloride or ammonium fluoride.

Although by way of example the application of two electrodes at one sideof-a semi-conductor body is described, the invention is not restrictedthereto. For instance also one or more than two electrodes at one sideor electrodes at different, -f.i., opposite sides, of a semiconductorbody may be applied using the inventionand a jig having apertures atopposite sides of the semi-conductor body. Jigs of this type, consistingof graphite, are well-known in the art, but such jigs are also usedduring the heating operation in melting the pellets. It is also known,especially in manufacturing germanium p-n-ptransistorsby meltingdonormaterials onto opposite sides of an n-type germaniumibody, to usean emitter pellet consisting of an indium-gallium alloy. In particularsuch an alloy 'containing'gallium, when in the molten state,

oftentends to adhere to graphite. By covering the germanium surface withan adhesive, f.i., as described above,

.and placing the body in ajig with apertures at opposite sides of thebody and introducing gallium containing pellets in the apertures suchthat they adhere to the germanium body by means of theadhesive, the jig.parts may be removed before any heating operation to melt the pellets iscarried out, such that in a subsequent heating to the use of asemi-conductor body consisting of germanium, butrmay be applied alsowhen semi-conductor that good results are obtained when adhering pelletsof aluminum or tin onto silicon bodies by means of a jig fand fusingthem subsequently to the silicon bodies withalloys and hard plastics asno restriction asresi'stance to heating is necessary.

What is claimed is: V

1. In the manufacture of a semiconductor device, a method of making analloy contact to a selected surface portion of a semiconductive body,comprising providing on the said surface portion a very thin layer of asolution of an adhesive which will substantially completely volatilizeupon heating and selected from the group consisting of oils, greases andfats in a solvent, which solvent rapidly evaporates at room temperatureleaving a thin layer of a member of the said group as an adhesivebehind, providing a jig containing an aperature over the said selectedsurface portion but spaced therefrom and disposing in said aperture ontothe adhesive-coated surface portion a mass of contact material capableof producing one of an ohmic and rectifying contact to thesemiconductive body to cause the mass to adhere to the said selectedsurface portion where the. contact is to be-made,

, hesive is neats-foot oil.

hesive is liquid paraffin.

thereafter removing the jig, thereafter heating the body with theadhering mass at a temperature at which the mass melts, wets and fusesto the said body surface portion and theadhesive volatilizes and issubstantially completely removed from the body, and thereafter coolingthe melt forming the desired alloycontact at the selected surfaceportion of the semiconductor.

2. A method as set forth in claim 1 wherein the solution furthercontains a flux to improve wetting which remains in the adhesive afterthe solvent has evaporated.

3. A method asset forth in claim 1 wherein the ad- 4. A method as setforth in claim 1 wherein the adlayer of a less than 1% solution of anadhesive which will completely volatilize upon heating and selected fromthe group consisting of oils, greases and fats in a solvent,

7 which solvent rapidly evaporates at roomtemperature group as anadhesive behind, providing a jig containing I leaving an extremely thinlayer of amember of the said an aperture over the said selected surfaceportion but "bodies of other material are used, for instance of silicon'or of an A B compound. Anyhow it has been found spaced therefrom anddisposing in said aperture onto the adhesive-coated surface portion amass of gallium-containing contact material capable of producing one ofan ohmic and rectifying contact to the semiconductivebody to cause themass to adhere to the said selected surface portion where the contact;is to .be m-ade, thereafter removing the jig, thereafter heating thebody with the ad ,hering mass at a temperature at which the mass melts,

out the use of a jig. Also in these cases very good results wereobtained when using an adhesive as mentioned above,such as neatsfoot oiladhesive solutionjinacetone :or a liquid paraffin adhesive solution intrichlorethene;

. Further the invention is not restricted to the choice of aspecialadhesiveor aspecial group of adhesives as jmany other wellknownadhesives may prove to-be of use in :the methods according'to theinvention, for instance gums, "starch and resinsmay be applied locallyin the semiconductorbody, preferably in such a manner that theseadhesives do nottouch any part of the jig. The jigs may consist of alarge variety of materials,

*' lsuch as'all ltinds ofwell-known suitablyworkableflmetals,

wets and fusesto the said body surface portion and the adhesive isvolatilized and completely removed from the body and thereaftercooling'the melt forming the desired alloy contact at the selectedsurf-ace portion of the semiconductor. I V j I 6'.-.A method as setforth in claim'5 wherein the ad- 7 hesive i'san oil produced as adistillate.

H References Cited in the file of this patent EUNITEDSTATES PATENTSKepple Mar. 27, 1956 2,825,667 Mueller Mar. 4, 1958 2,964,431 Kalish-n'Dec.l3,1960

1. IN THE MANUFACTURE OF A SEMICONDUCTOR DEVICE, A METHOD OF MAKING ANALLOY CONTACT TO A SELECTED SURFACE PORTION OF A SEMICONDUCTIVE BODY,COMPRISING PROVIDING ON THE SAID SURFACE PORTION A VERY THIN LAYER OF ASOLUTION OF AN ADHESIVE WHICH WILL SUBSTANTIALLY COMPLETELY VOLATILIZEUPON HEATING AND SELECTED FROM THE GROUP CONSISTING OF OILS, GREASES ANDFATS IN A SOLVENT , WHICH SOLVENT RAPIDLY EVAPORATES AT ROOM TEMPERATURELEAVING A THIN LAYER OF A MEMBER OF THE SAID GROUP AS AN ADHESIVEBEHIND, PROVIDING A JIG CONTAINING AN APERTURE OVER THE SAID SELECTEDSURFACE PORTION BUT SPACED THEREFROM AND DISPOSING IN SAID APERTURE ONTOTHE ADHESIVE-COATED SURFACE PORTION A MASS OF CONTACT MATERIAL CAPABLEOF PRODUCING ONE OF AN OHMIC AND RECTIFYING CONTACT TO THESEMICONDUCTIVE BODY TO CAUSE THE MASS TO ADHERE TO THE SAID SELECTEDSURFACE PORTION WHERE THE CONTACT IS TO BE MADE, THEREAFTER REMOVING THEJIG, THEREAFTER HEATING THE BODY WITH THE ADHERING MASS AT A TEMPERATUREAT WHICH THE MASS MELTS, WETS AND FUSES TO THE SAID BODY SURFACE PORTIONAND THE ADHESIVE VOLATILIZES AND IS SUBSTANTIALLY COMPLETELY REMOVEDFROM THE BODY, AND THEREAFTER COOLING THE MELT FORMING THE DESIRED ALLOYCONTACT AT THE SELECTED SURFACE PORTION OF THE SEMICONDUCTOR.